In vehicle equipment control systems such as disclosed in JP 2002-201838A, an in-vehicle unit communicates with a portable unit carried by a vehicle user as an electronic key so that vehicle door locking and unlocking, steering unlocking, engine starting or the like may be controlled from remote locations. In some systems, this control is performed automatically as long as the user carries it with him without any manual operations on the portable unit by the user. As such it is likely that the user often forget where the portable unit is located in a vehicle.
It is proposed therefore to divide a vehicle compartment into a plurality of communication areas and provide a plurality of radio transmitters, which cover the divided areas, respectively. The transmitters are driven to transmit request signals in the compartment when a portable unit is to be located. When a response signal of the portable unit is received by any one of the transmitters, the location of the portable unit is specified based on which transmitter has received the response signal. This location is notified to the user by a display or a voice message. This system, however, requires more transmitters as the number of communication areas is increased to more finely specify the location of the portable unit.